The present disclosure brings together two problems dealing with automobiles. The first issue concerns testing for leaks in an automotive evaporative emission control system. Gasoline in an automobile fuel tank evaporates over time, releasing vapors of volatile organic compounds. Apart from wasting fuel, evaporation may lead to malfunctions or in some cases, even an explosion, and in any event volatile organic compound vapors can be important pollutants. To prevent these occurrences, automotive vehicles are equipped with evaporative emission control systems which prevent the vapors from escaping.
Evaporative emission control systems are designed to capture and store gasoline vapor emissions during normal vehicle operation. The same system also captures gasoline vapors during refueling. Contemporary vehicles include onboard diagnostics, a vehicle's self-diagnostic and reporting capability which check and report on a number of vehicle subsystems, providing results accessible by the vehicle owner or a repair technician. Within this general category, fuel leaks may be addressed by a process referred to as leak diagnostics.
One method for performing leak diagnostics, the engine-off-natural-vacuum method, takes advantage of the fact that negative pressure is created when heated fuel cools. Thus, one may measure air pressure within the evaporative emission control system after the engine has been stopped for a time, identifying a leak if negative pressure does not occur. This method has limited effectiveness on hybrid vehicles, however. Because such vehicles have limited engine run times they reject minimal heat into the fuel tank, in turn minimizing the pressure buildup within the evaporative emission control system. Unable to employ the cool-down test, hybrid vehicles typically utilize expensive vacuum pumps to supply negative pressure for performing leak diagnostics.
A second problem involves flat tires. Traditionally, one addressed this problem by removing the flat tire and replacing it with the spare tire. As tire quality improved, reducing the instances of flat tires, automobile manufacturers began replacing the spare tire with a special, short-duty tire to be used only long enough to reach a service station. More recently, an expanding foam was introduced that could be injected into a flat tire. The expanding foam would both inflate the tire and plug the leak. Such products are readily available to consumers in the form of dispenser cans, such as the FIX-A-FLAT foam provided by Pennzoil and widely available in auto-parts stores.
Recently, automobile manufacturers have taken the next step, dispensing with a spare tire altogether in favor of the expanding foam. The foam is typically provided by the manufacturer as part of a flat tire repair kit, including an air pump and a dispensing can for the expanding foam. This unit is provided with the automobile by the manufacturer, and it usually remains within its specially provided storage location in the vehicle itself to deal with the rare emergency of a flat tire. Because such occurrences are rare, the flat tire repair kit may never be used at all throughout the life of the vehicle.
Accordingly, it can be seen that a need remains for an emission control system that accurately performs leak diagnostics in a cost-effective manner.